This application claims the benefit of Japanese Application No. 2001-255072 filed Aug. 24, 2001, in the Japanese Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium that can be installed in various magnetic recording apparatuses.
2. Description of the Related Art
Accompanying increases in capacity of magnetic disk recording apparatuses, there have been heightened demands to increase a recording density of magnetic recording media. A longitudinal magnetic recording method occupies a mainstream among conventional magnetic recording methods, but recently a perpendicular magnetic recording method has started to attract attention as an art to increase the recording density of the magnetic recording media.
Elements of a perpendicular magnetic recording medium include a magnetic recording layer of a hard magnetic material, and an under layer formed from a soft magnetic material that concentrates magnetic flux generated by the magnetic head used in recording into the magnetic recording layer. At present a CoCr type alloy crystalline film is predominantly used as a material for the magnetic recording layer used in the perpendicular magnetic recording medium. With such a film, a maximum value of the coercivity (Hc) is about 4000 Oe at present. Although to further increase the recording density it is necessary to further increase Hc, there are technical difficulties in fulfilling this demand.
On the other hand, a rare earth-transition metal alloy amorphous film that is used as a material for magneto-optical recording has a high perpendicular magnetic anisotropy constant Ku, and hence this film is extremely promising as a material for the magnetic recording layer of the perpendicular magnetic recording medium. However, in magneto-optical recording, a composition close to a compensation point is used, and Hc for such a composition is considerable larger than the Hc required of a material for perpendicular magnetic recording, and hence it is problematic to use the rare earth-transition metal alloy amorphous film as a perpendicular magnetic recording medium.
Various objects and advantages of the invention will be set forth in part in the description that follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
A Co type alloy crystalline magnetic recording material has a columnar structure in which crystal grains grow in a film thickness direction, which is a main cause of noise originating from a magnetic recording medium during recording and playback. As a recording density is increased in the future, influence of a crystal grain boundary on recorded signals will come to account for a larger and larger proportion.
Attempts are being made to reduce the influence of the crystal grain boundary by, for example, making a size of the crystal grain very small, but if the size of the crystal grain becomes too small, then a thermal stability of the recorded signal deteriorates abruptly, and in some cases a so-called xe2x80x9cthermal fluctuationxe2x80x9d problem in which a recorded signal vanishes may arise.
On the other hand, in the case that a rare earth-transition metal alloy amorphous film is used, due to being amorphous, the crystal grain boundaries do not exist, and hence the above problem does not arise. However, because the crystal grain boundaries do not exist there is nothing to act as a nucleus to keep a recorded signal in place, and hence there is a problem that the recorded signal may shift or vanish. In particular, the recorded signal may shift or vanish when recording at a high frequency. Hence, the rare earth-transition metal alloy amorphous film cannot be used as is, as a material for perpendicular magnetic recording to increase recording density.
In view of such problems, it is an object of the present invention to provide a perpendicular magnetic recording medium according to which there is no shift or loss of the recorded signals even in the case of high recording density using the rare earth-transition metal alloy amorphous film, and moreover, productivity is excellent.
Regarding an embodiment of the present invention, perpendicular magnetic recording medium, including: a soft magnetic under layer; an intermediate layer; a magnetic recording layer including a rare earth-transition metal alloy amorphous film and at least one of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, C and Si uniformly dispersed in the rare earth-transition metal alloy amorphous film; a protective layer; a liquid lubricant layer; and a nonmagnetic substrate, wherein the soft magnetic under layer, the intermediate layer, the magnetic recording layer, and the protective layer are built up in a predetermined order on the nonmagnetic substrate.
Moreover, an embodiment in accordance with the present invention a perpendicular magnetic recording medium, including: a soft magnetic under layer, an intermediate layer, a magnetic recording layer including a rare earth-transition metal alloy amorphous film and at least one boride of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al or Si uniformly dispersed in the rare earth-transition metal alloy amorphous film; a protective layer; and a nonmagnetic substrate, wherein the soft magnetic under layer, the intermediate layer, the magnetic recording layer, and the protective layer are built up in a predetermined order on the nonmagnetic substrate.
Moreover, an embodiment in accordance with the present invention provides a perpendicular magnetic recording medium, including: a soft magnetic under layer; an intermediate layer; a magnetic recording layer including a rare earth-transition metal alloy amorphous film and at least one carbide of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al or Si uniformly dispersed in the rare earth-transition metal alloy amorphous film; a protective layer; a liquid lubricant layer; and a nonmagnetic substrate, wherein the soft magnetic under layer, the intermediate layer, the magnetic recording layer, and the protective layer are built up in a predetermined order on the nonmagnetic substrate.
Moreover, a concentration of the at least one of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, C and Si or boride or carbide thereof in the rare earth-transition metal alloy amorphous film is at least 1% but not more than 20%.
Moreover, an underlayer; and a magnetic domain controlling layer, wherein the underlayer and the magnetic domain controlling layer are between the nonmagnetic substrate and the soft magnetic under layer.
As described above, according to an embodiment of the present invention, a perpendicular magnetic recording medium includes a soft magnetic under layer, an intermediate layer, a magnetic recording layer, a protective layer and a liquid lubricant layer built up in a predetermined order on a nonmagnetic substrate, wherein the magnetic recording layer is made of a rare earth-transition metal alloy amorphous film, which includes at least one of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, C and Si or a boride or a carbide uniformly dispersed through the rare earth-transition metal alloy amorphous film. As a result, compared to a case where the perpendicular magnetic recording medium is produced without adding element(s) Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, Al, C and/or Si, extremely good characteristics can be obtained at a high recording density. It is necessary to make a concentration of the element(s) or the boride(s) or the carbide(s) to be between 1% and 20%, and even if a plurality of additives (i.e., the element(s) or the boride(s) or the carbide(s)) are added at the same time, the perpendicular magnetic recording medium exhibiting good characteristics can be produced.
Moreover, by providing one or a plurality of underlayers and an antiferromagnetic layer for magnetic domain control of the soft magnetic under layer between the nonmagnetic substrate and the soft magnetic under layer, spike noise due to a magnetic domain wall formation in the soft magnetic layer can be completely suppressed, which is extremely desirable when making the perpendicular magnetic recording medium fit for practical use.
Furthermore, the method of manufacturing the perpendicular magnetic recording medium of the present invention can be carried out using an existing manufacturing apparatus, and hence this method is suited for mass production of high-capacity magnetic recording media.
These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.